1. Field of the Invention
The present invention is related to a frequency calibration circuit for automatically calibrating frequency and method thereof, and particularly to a frequency calibration circuit for automatically calibrating frequency according to an end-of-packet and a SYNC pattern of a low-speed Universal Serial Bus and method thereof.
2. Description of the Prior Art
An oscillator is one component found in many electronic products. Periodic waves generated by oscillators may be employed as carriers in communication systems, as timers or counters in computers or control systems, and as signals with different clocks used to control other circuits in microprocessors.
Generally speaking, frequencies generated by crystal oscillators, such as quartz oscillators, are more accurate, but system vendors often use less accurate non-crystal oscillators, such as resistor-capacitor (RC) oscillators, due to lower cost. The prior art uses corrected parameters to program non-volatile memories, such as an erasable programmable read only memory (EPROM), an electrically-erasable programmable read-only memory (EEPROM), and a flash memory, during production of the non-volatile memories, or uses laser-trimming to calibrate the frequency of the RC oscillator. However, regardless of whether the corrected parameters are written to the non-volatile memory or the laser-trimming is employed, additional cost is incurred.